RNA viruses depend on the interaction of their genomes with viral and cellular proteins to carry out many of the steps in their life cycle. The long-term objective of this proposal is to understand molecular mechanisms of interaction between viral RNAs and viral and cellular proteins. The specific aims of the proposal are designed to characterize the interactions of West Nile and Dengue virus RNAs with eEF-1A, and of hepatitis C virus (HCV) RNA with the HCV core protein. Cellular proteins have been reported to be present in the replication complexes of many viruses. However, for most of these proteins, the role they play in viral replication remains unknown. The studies presented here to characterize the interaction between eEF-1A and two important flaviviruses represent the initial steps in the elucidation of the role of eEF-1A in the life cycle of these viruses. The interaction between the HCV core protein and the RNA genome could be important for viral encapsidation. In addition, it could also be involved in other processes such as genome replication and translation of the viral mRNA. Identifying the specific domains and sequences that are involved in this interaction is an important step in order to better understand the virus life cycle. Gel shift assays, as well as footprinting experiments will be done in order to characterize the RNA-protein interactions. HCV infection is widely spread across the world, as it is estimated that approximately 3% of the world population is infected. Dengue virus infects more than 100 million cases of Dengue fever annually, and West Nile virus recently emerged in North America for the first time. Therefore, the elucidation of the molecular mechanism of interaction between the RNA and proteins of these viruses could be important in order to design effective antiviral therapies.